1. Field of the Invention
The present invention relates to a charged particle beam pattern writing apparatus, and an apparatus and method for correcting a dimension error of a pattern. For example, it relates to a method of previously resizing a pattern by using a pattern dimension change amount produced by the loading effect when performing a pattern forming after writing using electron beams, and to an apparatus and method for writing a pattern on a target workpiece by using electron beams on the basis of resized pattern data.
2. Description of Related Art
The lithography technique that advances microscale semiconductor devices is extremely important as being the only process of forming patterns in semiconductor manufacturing processes. In recent years, with high integration of large-scale integrated circuits (LSI), critical dimensions required for semiconductor device circuits are shrinking year by year. In order to form a desired circuit pattern on semiconductor devices, a master pattern (also called a mask or a reticle) of high precision is required. The electron beam writing technique intrinsically having excellent resolution is used for producing such highly precise master patterns.
FIG. 11 is a schematic diagram illustrating operations of a variable-shaped electron beam (EB) type writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus, including two aperture plates, operates as follows: A the first aperture plate 410 has a rectangular opening or “hole” 411 for shaping an electron beam 330. This shape of the rectangular opening may also be a square, a rhombus, a rhomboid, etc. A second aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 that passed through the opening 411 into a desired rectangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shaped opening 421 and thereby to irradiate a target workpiece or “sample” 340 mounted on a stage which continuously moves in one predetermined direction (e.g. X direction) during the writing or “drawing.” In other words, a rectangular shape formed as a result of passing through both the opening 411 and the variable-shaped opening 421 is written in the writing region of the target workpiece 340 on the stage. This method of forming a given shape by letting beams pass through both the opening 411 and the variable-shaped opening 421 is referred to as a “variable shaped” method.
In the electron beam writing mentioned above, highly precise uniformity of the line width is required on the surface of a target workpiece, such as a mask surface, when writing a pattern on the target workpiece. However, in the electron beam writing, a phenomenon called a proximity effect occurs when electron beams irradiate a circuit pattern on a mask where resist is applied. The proximity effect is generated by the backward scattering of electron beams penetrating a resist film, reaching the layer thereunder to be reflected, and being incident into the resist film again. As a result, a dimension change occurs, thereby causing a pattern being written in dimension deviated from a desired one. On the other hand, after writing a pattern, when developing the resist film or etching the layer thereunder, a dimension change called a loading effect due to density difference of a circuit pattern occurs.
As the loading effect being a dimension change occurring in a charged particle beam writing represented by an electron beam writing, the following can be cited as examples: a loading effect generated when developing a resist film, a loading effect generated when etching chromium (Cr) serving as a shading film under a resist film, and a loading effect generated when a pattern dimension change is produced by chemical mechanical polishing (CMP). In the electron beam writing, further highly precise uniformity of the line width in a mask surface is required with narrowing the line width of a pattern. Therefore, a loading effect correction to correct the dimension change due to the loading effect is needed. Thus, writing is performed using a dimension obtained by resizing the design line width of a circuit pattern (design pattern) so that a dimension change amount (dimension error) due to a loading effect may be estimated, and thereby a desired design line width can be obtained through the loading effect produced in etching etc. For example, when a calculated dimension change amount caused by the loading effect is positive (direction of the line width becoming wide), the circuit pattern is projected after being resized so that the line width may become narrower than the design line width by the dimension change amount produced by the loading effect.
As to the loading effect correction, it is disclosed that a pattern data correction amount is calculated by adding a loading effect correction amount for correcting a dimension change produced in etching to a process resizing amount for correcting a pattern shape error produced in writing and developing (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2004-279950).
When resizing a pattern in order to correct the loading effect mentioned above, it is essentially necessary to calculate influence of the loading effect based on a pattern after resizing. This is because the sum of the amount of the influence (dimension error) and the dimension of the resized pattern should be in accordance with the design dimension. However, conventionally, influence of the loading effect is calculated based on a pattern before resizing, i.e., a pattern with the design dimension, and resizing is performed by correcting the pattern by the amount of the influence (dimension error). This conventional method can be adequately realized on the premise that the amount of correction is sufficiently small with respect to the pattern before correction and that an error produced in writing with the resized pattern can be disregarded. However, with the recent trend of pattern miniaturization, it is envisaged that such an error could not be neglected.